Extrusion die mask

ABSTRACT

A mask or face plate, having an orifice or opening formed therethrough of desired size and configuration, is positioned against the discharge face of an extrusion die. The mask restricts the flow of extrudable material through the die so that such material will conform to the size and configuration of the opening or orifice formed through the mask. A recess formed in the face of the mask adjacent the discharge face of the extrusion die, surrounds the orifice formed therethrough, and communicates with said orifice by means of a gap formed in the inlet face of the mask between said recess and said orifice. The method of extrusion set forth with respect to the recessed or scalloped mask has particular utility when utilized with an extrusion die for forming cellular or honeycomb structures, in that the predetermined gap meters a controlled flow of additional batch material from the recess to the outer boundaries of the extruded honeycomb article passing through the orifice in said mask to encapsulate the honeycomb structure with a smooth uniform skin having improved isostatic crushing strength.

This is a division of application Ser. No. 532,362, filed Dec. 13, 1974,now U.S. Pat. No. 3,947,214.

BACKGROUND OF THE INVENTION

This invention pertains to the art of manufacturing extruded articlesfrom extrudable material such as ceramic batches and similar materialswhich have the property of being able to flow or plastically deformduring extrusion, while being able to become sufficiently rigidimmediately thereafter so as to maintain their structural integrity.More particularly, the present invention relates to an improvedextrusion die mask utilized in conjunction with an existing extrusiondie, for not only providing such extrusion die with greater versatility,but also for improving skin characteristics about cellular or honeycombarticles which may be extruded by such die.

The extrusion die may be of virtually any known construction, howeverthe extrusion die mask of the present invention has particularapplication with respect to extrusion dies having multiple core pins forforming cellular or honeycomb structures, such as disclosed in U.S. Pat.No. 3,790,654. That is, such extrusion dies for making honeycombstructures necessitate the formation of numerous core pins, andaccordingly the manufacture of such dies is not only very complex butquite costly. Further, every time a honeycomb structure having a newsize or shape is required, it necessitates the burdensome manufacture ofan additional new costly die. Not only does this require the maintenanceof a relatively large inventory of extrusion dies with different sizesand configurations, but also many of such dies become obsolete as sizeand shape requirements are varied.

U.S. Pat. No. 3,836,302 discloses a mask or face plate for overlying aportion of the discharge face of an extrusion die so as to provide suchdie with greater flexibility and variability. The mask of said inventiondid in fact function satisfactorily to provide extrusion dies withgreater flexibility and variability, and when such mask was utilizedwith dies for forming honeycomb structures, they also provided anintegral skin or casing about such structures. However, during theformation of the skin about the honeycomb structures, the mask had atendency to crush peripheral cells as the structure passed through thecentral opening of the mask. Further, the surface of the skin producedby such mask had a tendency to be fairly rough, and was not of acharacter to provide a high degree of isostatic crushing strength.

Accordingly, the present invention has overcome the problems of roughskin texture, peripheral cell distortion, and low isostatic crushingstrength which resulted from the utilization of the mask or face plateof the prior art, by providing an improved extrusion die mask having arecess reservoir and a flow control or metering gap in its inlet facefor forming a substantially smooth integral skin about a honeycombarticle without causing peripheral cell distortion and with improvedisostatic crushing strength.

SUMMARY OF THE INVENTION

In its simplest form, the present invention is directed to a face plateor mask for overlying a portion of the discharge face of an extrusiondie so as to provide an article extruded by such die with an integralskin of desired thickness, texture, and improved strength.

The invention has particular application for use with extrusion dies forforming thin walled cellular or honeycomb structures which are providedwith an integral shell or casing about the honeycomb network. Cellularor honeycomb structures refer to any structure having a plurality ofopenings or passages of any desired size or shape extendingtherethrough, and the present invention provides the advantage of beingable to form a plurality of such structures with different sizes andshapes from a single extrusion die while simultaneously providing abounding wall or shell about the desired shape with a predeterminedthickness and surface texture.

The mask or face plate of the present invention has a blocking surfacepositioned adjacent the discharge surface of an extrusion die so as toblock or mask-off the discharge flow of extrudable materials which wouldnormally flow through the masked-off portion of the extrusion die. Anopening or orifice of desired size and configuration is formed centrallythrough the mask such that the inlet end of such orifice is in directcommunication with the discharge face of the extrusion die. An annularrecessed reservoir or scalloped portion is formed in the blockingsurface about the orifice, and communicates with an inlet portion of theorifice by means of a predetermined gap. Since the mask has particularutility when utilized with extrusion dies for forming honeycombstructures by providing an integral skin thereabout, the predeterminedgap is of great significance in view of the fact that it controls thethickness of the skin applied about the outer periphery of the honeycombarticle. Accordingly, batch material extruded adjacent the periphery ofthe inlet end of the orifice is received within the annular reservoirand controllably fed by means of the predetermined gap to a tapered orchamfered inlet portion of the orifice for forming a skin about theextruded honeycomb article passing therethrough. The mask will alsofunction with a straight inlet, that is, without a taper or chamfer.Masks of the present invention are removably mounted to the diestructure so as to be readily interchangeable with different extrusiondies, thus providing a greater degree of flexibility in theirutilization.

It thus has been an object of the present invention to provide a novelextrusion method for existing extrusion dies so as to provide greaterflexibility and variability in the dies and configurations of theextruded product which may be formed from such dies.

A further object of the present invention has been to provide a novelmethod for utilizing existing extrusion dies which form honeycombstructures, to form such structures with different sizes andconfigurations while simultaneously forming a substantially smoothintegral skin or casing thereabout with improved isostatic crushingstrength and without materially distorting peripheral cells about thehoneycomb structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view in section of an extrusion die assemblyincluding the extrusion die mask of the present invention.

FIG. 2 is a top plan view of the mask shown in FIG. 1.

FIG. 3 is a cross sectional view in elevation taken along line 3--3 ofthe mask shown in FIG. 2.

FIG. 4 is an enlarged fragmental elevational view partially in sectionillustrating the configuration and positionment of the recessedreservoir and gap formed in the extrusion die mask relative to theextrusion die.

FIGS. 5, 6, 7, 8, and 9 illustrate further embodiments of the recessedreservoir which may be formed in the face of the extrusion die mask.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly FIG. 1, an extrusion dieapparatus 10 is shown including a support structure 12 for a cylinder14, housing an extrusion chamber 16. An extrusion die 18 of any desiredconfiguration is positioned adjacent the outlet end of the extrusionchamber 16. Since the present invention has particular application withrespect to extrusion dies for forming honeycomb structures, such a dieis shown for purposes of illustration. The die body 18 has an inlet face20 provided with a plurality of openings or feed passageways 22, and anoutlet face 24 which may be provided with a plurality of interconnecteddischarge slots 26. The feed passageways 22 communicate with selectedareas of the discharge slots 26 so as to deliver the batch material fromthe extrusion chamber 16 to the discharge slots 26. The interconnecteddischarge slots 26 form a grid work through which the batch material isextruded to form the matrix of the coherent honeycomb structure.

An extrusion die mask 32 is positioned adjacent the outlet face 24 ofthe extrusion die 18 and is removably secured in position adjacent theoutlet face by means of a retaining ring 34 and a plurality of bolts orcap screws 36. The mask 32 has a blocking surface 38 which is positionedadjacent the outlet face 24 of the die 18 and surrounds a centralopening or orifice 40 of desired size and configuration extendingthrough the mask 32. An annular recess or reservoir area 42 is formed inthe blocking surface 38 about an inlet portion 44 of orifice 40. Theannular recess 42 is radially outwardly offset with respect to orifice40, and communicates therewith by means of a predetermined channel orgap 46 formed in blocking surface 38 between the inlet portion 44 oforifice 40 and the annular recess 42. As shown, the inlet portion 44 ispreferably tapered so as to facilitate the flow of batch materialdelivered by gap 46 from the reservoir area 42 to the orifice 40,however, the mask will also function without a tapered inlet.

Whereas the blocking surface 38 restricts the flow of extrudablematerial through the die 18 to those areas of such die which are in opencommunication with the orifice 40, the annular recess or reservoir area42 provides a supply of batch material which is controllably fed by thepredetermined gap 46 to the orifice 40 for forming a skin about thehoneycomb article extruded through die 18. The orifice 40 may have achamfered outlet end 48 for facilitating the withdrawal of the extrudedarticle. Further, a peripheral positioning rim 50 may be formed onblocking surface 38 for positionment within an aligning recess 52 formedin the outlet face 24 of die 18.

Although the cross sectional shape of the annular recess or reservoirarea 42 may vary as shown in FIGS. 5 through 8 inclusive, the contour ofthe reservoir as shown in FIGS. 1 through 4 inclusive is presentlypreferred. As will be apparent from FIG. 4, the preferred contour is inthe form of a shallow recess formed by striking the curvature from acenter of radius positioned above the blocking surface. The contours ofthe recessed portion 42 of FIGS. 5 and 6 are characterized by beingsubstantially deeper than that of FIG. 4, since the centers of radiusfor their curvatures are below the blocking surface 38. In FIG. 6, thegap 46 is characterized by a pointed ridge rather than a flat surface asdisclosed in the other embodiments. FIG. 7 discloses a recessed orreservoir area 42 having a rectangular cross sectional configuration,whereas FIG. 8 discloses such reservoir area having a triangular crosssectional configuration, and FIG. 9 discloses the reservoir area havinga wedge shaped cross sectional configuration.

The smoothly curved contour of the recess 42 is preferred forfacilitating the flow of batch material from the die 18 into thereservoir and then outwardly through metering channel or gap 46 into theorifice 40 for forming a skin about the outer boundary of the honeycombarticle extruded by die 18 and passed through orifice 40. The thicknessof the skin formed on the honeycomb article is controlled by the gapdepth 46. That is, by increasing the gap depth, a thicker skin or outercasing can be provided about the extruded article, whereas a reductionin the depth of gap 46 will produce a thinner skin. In view of the factthat the batch material from die 18 which flows into reservoir 42 iscompacted within the reservoir before flowing outwardly through themetering gap 46, the batch from reservoir 42 provides a solid continuoussmooth-surface skin about the honeycomb article without crushing ormaterially distorting peripheral cells of the article, as was commonwith a prior art device. Accordingly, with the mask of the presentinvention it is possible to provide improved isostatic crushing strengthto the honeycomb articles. In fact, using substantially identical batchcompositions and extrusion procedures, it has been found that throughthe utilization of the mask of the instant invention, over that of theprior art, isostatic crushing strengths have increased on the order of100 to 250 psi.

Although the orifice 40 is shown in FIG. 2 in the shape of a circle, thesize and configuration thereof may vary as desired, and may includevirtually any geometric shape such as oval, square, triangular,eliptical, etc. Further, it will be appreciated that the variousdimensions of the orifice may vary considerably with the material beingextruded, however, the following specific example is given as anillustration for extruding a clay type of material. A stainless steelmask was formed having a circular orifice provided with an inlet portionhaving a 25° taper with the axis of extrusion and extending from a flatgap surface to the periphery of the main orifice having a diameter ofabout 41/4inches. The gap had a depth of 0.015 inches and the annularrecess had a radius of 3/32 inch with a radius center above the blockingsurface, so as to form a recess depth of about 0.05 inches. Claymaterial was extruded through a known honeycomb die and passed throughthe circular orifice of the mask, with peripheral portions of theextruded material being collected within the annular recess and meteredthrough the gap to form a cylindrical honeycomb structure having asmooth integral outer skin with a thickness of about 0.015 inches. Thecells about the periphery of the extruded article were not deformed andvirtually identical to interior cells, and the article after firing hadan isostatic crushing strength of about 480 psi.

It will be understood that the foregoing example merely sets forth a nowpreferred embodiment whereas the metering channel or gap may vary asdesired to produce a predetermined thickness with gaps of about 0.01 toabout 0.06 providing operable results. Further, the depth of the recessmay be varied by either increasing or decreasing both the radius ofcurvature and the center of radius, when utilizing a curved recess, orby merely increasing or decreasing the depth per se when utilizing apolygonal recess. Further, it appears that the entrance angle may bevaried over rather wide limits, such as from 0° to 45°, withoutaffecting operability. That is, the mask will function with a zerodegree entrance angle, however to reduce corner wear an entrance angleis preferred.

Although the now preferred embodiments of the invention have been setforth, it will be apparent to those skilled in the art that variouschanges and modifications may be made thereto without departing from thespirit and scope thereof as defined in the appended claims.

I claim:
 1. A method of forming an integral skin about an extrudedhoneycomb article as the article is being extruded, comprising the stepsof extruding batch material through a die to form a honeycomb article,simultaneously collecting batch material extruded through said die in areservoir peripherally of said extruded article, flowing such collectedmaterial radially inwardly through a predetermined gap toward the outerperiphery of said extruded article, and forming an integral skin ofpredetermined thickness proportional to said predetermined gap on theouter periphery of said extruded article with the material flowingradially thereto.
 2. A method of forming an integral skin on a honeycombarticle as defined in claim 1 including the step of metering the flow ofsaid extruded batch material from said reservoir to the periphery of theextruded article by controlling the depth of said predetermined gap andthereby controlling the thickness of the skin applied to said extrudedarticle.